1. Field of the Invention
The invention concerns a technique for the removal of petroleum-based pollutants spilled on water, seas, lakes, rivers, etc, and a material designed for this usage.
2. Background of the Prior Art
Water pollution caused by spills of petroleum poses poorlyresolved problems, whether the pollution is widespread, as occurs as a result of shipwrecks, oil tankers, and "wild degasification" operations performed by these tankers, or pollution which is more localized, in particular on waterways.
Some conventional techniques make use of chemical agents which cause the dispersion or dissolution of the treated petroleum. In this case, the action taken is meant to minimize the damaging consequences of the oil, without, however, removing it.
Other methods call for attempts to remove the spilled oil. Various absorbent materials have been suggested for the conduct of operations of this kind. The material in question, which is spread at the surface of the polluted water, becomes loaded with oil. The absorbent material is retrieved and then destroyed, or at least stored at sites where it does not constitute too burdensome a problem
To be used appropriately for the petroleum-absorption operation, the material selected must possess the following properties.
It must have good affinity for the oils normally encountered in this type of pollution and it must not be highly water-absorbent and thus not liable to become loaded with water, to the detriment, in particular of the oil-absorption capability sought.
Independently of these intrinsic properties which directly involve the capacity to separate oil and water, the product must, in addition, meet other requirements. Among these latter, it is essential that the material used be capable of easy retrieval, and consequently, that it float on the surface of the water. It must be possible, moreover, to keep the material under reduced volume and, if possible reduced weight, both to facilitate transport to the site where it will be used and to minimize storage costs. Finally, it is essential that the cost of the material be the lowest possible. This last requirement removes from consideration a large quantity of synthetic materials, including polyurethane foam, expanded polystyrene granules, or non-woven materials made of polypropylene or similar fibers.
The use of mineral wools has also been proposed. U.S. Pat. No. 4,006,079 thus describes the use of glass wool felts reinforced by a frame which provides cohesiveness. The felts are packaged in rolls, which are spread out over the surface of the oil slick to be absorbed. They are then taken up, still in the form of strips, after being impregnated with the petroleum. The use of this type of product is closely restricted by very specific requirements which do not lend themselves to ease of implementation. Furthermore, the use of a frame to reinforce the felt substantially complicates packaging and adds to the cost of the product.
The use of mineral wool for absorbing oil or petroleum products has, again, been proposed in British Patent 1,235,463 and in French Patent 2,457,345. These two documents describe the use of mineral wool in different forms, especially as granules of limited sizes.
While the advantage of felts made of mineral fibers for the absorption of petroleum products spilled on water is widely recognized, especially because of the relatively moderate costs of the products used, it is also known that this type of product possesses at least one disadvantage. Indeed, while the mass of the oil thus recovered in relation to the mass of the fibers used is relatively large, the volume of the fibers in relation to their weight is very high. In other words, a sizable volume of the product must be stored and transported.
To limit this problem, it is asserted that the felts used may be compressed. As regards normal felt, such as those described in these previous patents, it appears, however, that the compression rate remains limited. The compression rate of the mineral felts specified in the last two documents does not ordinarily exceed 4 or 5. One is, therefore, dealing with low-density products which, given their absorptive capacity, are relatively cumbersome.